JP2015064915A - Method of manufacturing glass substrate for information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for an information recording medium capable of securing a larger flat region of a principal surface than the conventional method.SOLUTION: In the method of manufacturing a glass substrate for an information recording medium, the crystal grain size of the glass substrate before a polishing process is 1 nm or more and 20 nm or less, the polishing amount of a surface in the polishing process is 5 μm or more and 40 μm or less, and the specific modulus of the glass substrate is 33.5 GPa cm/g or more and 36.5 GPa cmor less.

Description

  The present invention relates to a method for producing a glass substrate for an information recording medium.

  Information recording devices are built into various devices such as computers. In such an information recording apparatus, a disk-shaped information recording medium (also referred to as a magnetic disk) is mounted. The information recording medium includes a glass substrate and a magnetic recording layer formed on the main surface of the glass substrate. In recent years, smartphones and tablet devices have become widespread. An information recording apparatus is required to have a larger storage capacity, and an information recording medium is required to have a higher recording density (for example, a recording density of 600 Gbit / in 2 or more).

  In order to meet such a demand, for example, it is necessary to increase the area of a recordable area (magnetic recording layer) of one magnetic disk as much as possible. In order to realize this, it is necessary to form a recordable region closer to the outer peripheral end of the glass substrate. However, in the vicinity of the outer peripheral edge portion of the glass substrate, there is a fact that a bulge (ski jump) in which the surface rises with respect to the main surface and a roll-off (surface droop) in which the surface falls with respect to the main surface are easily formed.

  Japanese Patent Laying-Open No. 2009-220719 (Patent Document 1) discloses a method for manufacturing a glass substrate for a magnetic disk, in which the surface roughness and micro-waviness on the substrate surface are in a predetermined range and relationship.

JP 2009-220719 A

  The inventors of the present application produced a magnetic disk (information recording medium) having a radius of 32.5 mm using a conventional manufacturing method using crystallized glass. In this conventional manufacturing method, after a rough polishing process is performed on a glass substrate, a chemical strengthening process is performed on the glass substrate.

  When a magnetic disk was incorporated into a hard disk and a hard disk read / write test was performed using this hard disk, there was no major problem in electromagnetic conversion characteristics in the region of the magnetic recording layer having a radius of 31.5 mm or less. It was found that read / write errors frequently occur in an area outside of .5 mm, making it difficult to use as a recording area.

  That is, in a glass substrate that has been subjected to a crystallization process, the polishing time is deteriorated due to the crystallization process, so that the polishing time is increased. As a result, the end surfaces (inner peripheral end surface and outer peripheral end surface) of the glass substrate are increased. The inventors of the present application have found that roll-off (sagging) is likely to deteriorate.

  An object of this invention is to provide the manufacturing method of the glass substrate for information recording media which can ensure the smooth area | region of a main surface widely compared with the past.

  The manufacturing method of the glass substrate for information recording media based on this invention is a manufacturing method of the glass substrate for information recording media by which crystallized glass is used for a glass substrate, Comprising: The shaping | molding process which shape | molds the said glass substrate, and the said shaping | molding A shape processing step of performing shape processing on the glass substrate following the step, and a polishing step of polishing the surface of the glass substrate following the shape processing step.

The crystal grain size of the glass substrate before the polishing step is 1 nm to 20 nm, the polishing amount of the surface in the polishing step is 5 μm to 40 μm, and the specific elastic modulus of the glass substrate is 33 It is not less than 5 GPa · cm ³ / g and not more than 36.5 GPa · cm ³ .

  In another embodiment, the radius of the glass substrate after performing the polishing step is r (mm), and the roll-off value at a position of r (mm) −0.5 (mm) is −100. (Nm) or more and 30 (nm) or less.

In another embodiment, the glass substrate is a crystallized glass containing spinel crystals or a crystallized glass containing MgO—TgO ² crystals.

In another embodiment, the glass substrate has a glass composition range of SiO ₂ of 54 wt% or more and 64 wt% or less, Al ₂ O ₃ of 12 wt% or more and 22 wt% or less, and B ₂ O ₃ of 1 wt% or more. 8 wt% or less, Na ₂ O is 1 wt% or more and 8 wt% or less, MgO is 5 wt% or more and 15 wt% or less, and TiO ₂ is 1 wt% or more and 8 wt% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass substrate for information recording media which can ensure the smooth area | region of a main surface widely compared with the former can be obtained.

It is a perspective view which shows an information recording device provided with the glass substrate manufactured by using the manufacturing method of the glass substrate for information recording media in embodiment. It is a top view which shows the glass substrate manufactured by using the manufacturing method of the glass substrate for information recording media in embodiment. It is arrow sectional drawing along the III-III line in FIG. It is a top view of the glass substrate for information recording media in which the magnetic recording layer was formed. It is arrow sectional drawing along the VV line in FIG. It is a flowchart which shows the manufacturing method of the glass substrate for information recording media in embodiment. It is a figure which shows the HDD test result of each Example and each comparative example. It is a figure which shows the roll-off of the glass substrate used in each Example and each comparative example. It is a figure which shows the composition of the glass substrate used in each Example and each comparative example.

  Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and the examples, when the number, amount, and the like are referred to, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the description of the embodiment and each example, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Information recording device 30)
The information recording device 30 will be described with reference to FIG. FIG. 1 is a perspective view showing the information recording apparatus 30. The information recording apparatus 30 includes the glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium (hereinafter also simply referred to as a glass substrate) in the embodiment as the information recording medium 10.

  Specifically, the information recording device 30 includes an information recording medium 10, a housing 20, a head slider 21, a suspension 22, an arm 23, a vertical shaft 24, a voice coil 25, a voice coil motor 26, a clamp member 27, and a fixing screw. 28. A spindle motor (not shown) is installed on the upper surface of the housing 20.

  An information recording medium 10 such as a magnetic disk is rotatably fixed to the spindle motor by a clamp member 27 and a fixing screw 28. The information recording medium 10 is rotationally driven by this spindle motor at, for example, several thousand rpm.

  The arm 23 is attached to be swingable about the vertical axis 24. A suspension 22 formed in a leaf spring (cantilever) shape is attached to the tip of the arm 23. A head slider 21 is attached to the tip of the suspension 22 so as to sandwich the information recording medium 10.

  A voice coil 25 is attached to the side of the arm 23 opposite to the head slider 21. The voice coil 25 is clamped by a magnet (not shown) provided on the housing 20. A voice coil motor 26 is constituted by the voice coil 25 and the magnet.

  A predetermined current is supplied to the voice coil 25. The arm 23 swings around the vertical axis 24 by the action of electromagnetic force generated by the current flowing through the voice coil 25 and the magnetic field of the magnet. As the arm 23 swings, the suspension 22 and the head slider 21 also swing in the direction of the arrow AR1. The head slider 21 reciprocates on the front and back surfaces of the information recording medium 10 in the radial direction of the information recording medium 10. A magnetic head (not shown) provided on the head slider 21 performs a seek operation.

  While the seek operation is performed, the head slider 21 receives a levitation force due to an air flow generated as the information recording medium 10 rotates. Due to the balance between the levitation force and the elastic force (pressing force) of the suspension 22, the head slider 21 travels with a constant flying height with respect to the surface of the information recording medium 10. By the traveling, the magnetic head provided on the head slider 21 can record and reproduce information (data) on a predetermined track in the information recording medium 10. The information recording apparatus 30 on which the glass substrate 1 is mounted as a part of the members constituting the information recording medium 10 is configured as described above.

(Glass substrate 1)
FIG. 2 is a plan view showing glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium according to the present embodiment. 3 is a cross-sectional view taken along the line III-III in FIG.

  As shown in FIGS. 2 and 3, a glass substrate 1 (glass substrate for information recording medium) used as a part of the information recording medium 10 (see FIGS. 4 and 5) has a first main surface 2 and a second main surface 2. It has a main surface 3, an inner peripheral end face 4 that defines a hole 5, and an outer peripheral end face 6, and is formed in a disc shape as a whole.

  The hole 5 is provided so as to penetrate from the first main surface 2 toward the second main surface 3. The inner peripheral end surface 4 includes a straight portion 4a and a chamfered portion 4b. The chamfered portion 4b includes an inner peripheral end chamfer portion formed between one main surface 2 and the straight portion 4a, and an inner peripheral end chamber formed between the other main surface 3 and the straight portion 4a. Including the fur part.

  The outer peripheral end surface 6 includes a straight portion 6a and a chamfered portion 6b. The chamfered portion 6b includes an outer peripheral end chamfer portion formed between one main surface 2 and the straight portion 6a, and an outer peripheral end chamfer portion formed between the other main surface 3 and the straight portion 6a. Including.

  The glass substrate 1 has a size of 0.8 inch, 1 inch, 1.8 inch, 2.5 inch or 3.5 inch, for example. The glass substrate 1 has a thickness of 0.3 mm, 0.635 mm, 0.8 mm, 1 mm, 2 mm, and 2.2 mm, for example. The thickness of the glass substrate 1 is a value calculated by averaging the values measured at a plurality of arbitrary points that are point-symmetric on the glass substrate 1.

A glass composition of the glass substrate 1, that range, SiO ₂ is more than 54 wt% 64 wt% or less, _Al 2 _{O 3} is more than 12 wt% 22 wt% or _less, B 2 _{O 3} is more than 1 wt% 8 wt% or less, Na ₂ O may be 1 wt% or more and 8 wt% or less, MgO may be 5 wt% or more and 15 wt% or less, and TiO ₂ may be 1 wt% or more and 8 wt% or less.

Further, the specific elastic modulus of the glass substrate 1 is preferably 33.5 GPa · cm ³ / g or more and 36.5 GPa · cm ³ or less.

(Information recording medium 10)
FIG. 4 is a plan view showing an information recording medium 10 provided with a glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along the line VV in FIG.

  As shown in FIGS. 4 and 5, the information recording medium 10 includes a glass substrate 1 and a magnetic recording layer 14. The magnetic recording layer 14 is formed so as to cover predetermined regions of the first main surface 2 and the second main surface 3 of the glass substrate 1. The magnetic recording layer 14 may be provided only on the first main surface 2 (one side), or may be provided only on the second main surface 3 (one side).

  The magnetic recording layer 14 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the first main surface 2 and the second main surface 3 of the glass substrate 1 (spin coating method). The magnetic recording layer 14 may be formed by a sputtering method or an electroless plating method performed on the first main surface 2 and the second main surface 3 of the glass substrate 1.

  The film thickness of the magnetic recording layer 14 is about 0.3 μm to 1.2 μm in the case of spin coating, about 0.04 μm to 0.08 μm in the case of sputtering, and about 0.05 μm to about in the case of electroless plating. 0.1 μm. From the viewpoint of thinning and high density, the magnetic recording layer 14 is preferably formed by sputtering or electroless plating.

  As a magnetic material used for the magnetic recording layer 14, a Co-based alloy or the like containing Ni or Cr as a main component is added for the purpose of adjusting the residual magnetic flux density. Is preferably used. In recent years, Fe—Pt magnetic materials have come to be used as magnetic layer materials suitable for heat-assisted recording.

  In order to improve the sliding of the magnetic head, the surface of the magnetic recording layer 14 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

  The magnetic recording layer 14 may be provided with an underlayer or a protective layer as necessary. The underlayer in the information recording medium 10 is selected according to the type of magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

  The underlayer provided on the magnetic recording layer 14 is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer for preventing wear and corrosion of the magnetic recording layer 14 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, or a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus together with the underlayer and the magnetic film. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(Glass substrate manufacturing method)
Next, with reference to FIG. 6, the manufacturing method of the glass substrate 1 and the information recording medium 10 which concern on this Embodiment is demonstrated. FIG. 6 is a flowchart showing a method for manufacturing the glass substrate 1 and the information recording medium 10.

  In the present embodiment, a “chemical strengthening step” for forming a surface enhancement layer on the surface of the glass substrate is not employed. Specifically, the step of strengthening the surface of the glass substrate by replacing lithium ions and sodium ions on the surface of the glass substrate with sodium ions and potassium ions in the chemical strengthening solution, respectively, and forming a compressive stress layer, Not adopted.

(Molding process)
In the “forming step” of step 11 (hereinafter abbreviated as “S11”, the same applies to step 12 and subsequent steps), for example, a glass material is melted and the molten glass is poured into a planar mold. It is press-molded by sandwiching molten glass with a mold to produce a disk-shaped glass base material (precursor). A crystallized glass substrate can be obtained by press-molding and crystallizing an amorphous glass substrate (blanks material) between ceramic plates and heat-treating it.

The material of the crystallized glass to be prepared preferably contains crystals having a diameter (crystal diameter) of 1 nm or more and 20 nm or less. The crystal grain size referred to here is, for example, a value when the crystal grain size of crystallized glass is measured using a transmission electron microscope JEM-2000FX manufactured by JEOL Ltd. (average value of measurement number n = 50). is there. As a material of the crystallized glass to be prepared, it is preferable to include a spinel crystal or a MgO—TgO ² crystal.

(Shaping process)
The following steps S12 to S15 are shape processing steps for performing shape processing on the glass substrate following the heat treatment step. The steps from S12 to S15 are not limited to the order described below, and are in no particular order. Moreover, you may perform several times as needed.

  In the “coring step” of S12, a hole was formed in the center of the glass substrate using a cylindrical diamond drill to produce an annular glass substrate. The inner peripheral end surface and the outer peripheral end surface of the glass substrate were ground with a diamond grindstone, and a predetermined chamfering process was performed. In the polishing of the inner peripheral end face and the outer peripheral end face, the inner peripheral end face of the glass substrate was polished using a polishing brush having a spiral brush bristle material. As the abrasive grains, a slurry containing general cerium oxide abrasive grains (average particle diameter φ2 μm) was used. However, the present invention is not limited to this method, and the glass brush may be rotated in a state where the polishing brush is in contact with each end face while being immersed in the polishing liquid.

  In the “first lapping step” of S13, both main surfaces of the glass substrate were lapped. This first lapping step was performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen was pressed on both surfaces of the glass substrate from above and below, the grinding liquid was supplied onto the main surface of the glass substrate, and these were moved relatively to perform lapping. By this lapping process, a glass substrate having a substantially flat main surface was obtained.

  In the “second lapping step” of S14, lapping was performed on both main surfaces of the glass substrate in the same manner as in the first lapping step (S12). By performing the second lapping step, the fine uneven shape formed on the main surface in the coring and end face processing in the previous step can be removed in advance. As a result, the polishing time of the main surface in the subsequent process can be shortened.

  In the “inside / outside processing step” of S15, the end surfaces on the inner and outer periphery of the glass substrate were ground with a grindstone and mirror-polished by brush polishing. As the abrasive grains, a slurry containing general cerium oxide abrasive grains was used.

(Polishing process)
In the following S16 and S17, a polishing process is performed. In the present embodiment, two polishing steps are employed, but two or more polishing steps may be employed.

  In the “first polishing step” of S16, main surface polishing was performed. The first polishing step is mainly intended to correct scratches and warpage remaining on the main surface in the first and second lapping steps (S12, S14) described above. In the first polishing step, the main surface was polished by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, general cerium oxide abrasive grains were used.

  In the “second polishing step” of S17, both main surface polishing steps were performed. In the present embodiment, the first main surface 2 and the second main surface 3 of the glass substrate 1 are subjected to a polishing process with a thickness of 5 μm to 40 μm. In the second polishing step, polishing was performed by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, colloidal silica having an average particle diameter of about 20 nm was used to obtain a smooth surface.

  The polishing amount may be 5 μm or more and 40 μm or less in the total polishing amount in the “first polishing step” in S16 and the “second polishing step” in S17.

  In the “cleaning step” of S18, the main surface and the end surface of the glass substrate are cleaned. Thereby, the deposits remaining on the glass substrate are removed. Thereby, the glass substrate 1 shown in FIG. 2 and FIG. 3 is completed.

  In the “magnetic thin film layer forming step” of S19, after cleaning the glass substrate 1 obtained through the above-described steps, an adhesion layer made of a Cr alloy and a soft magnetic layer made of a CoFeZr alloy are formed on both main surfaces of the glass substrate 1. An information recording medium of a perpendicular magnetic recording system was manufactured by sequentially forming an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a C-based protective layer, and an F-based lubricating layer. This configuration is an example of a configuration of a perpendicular magnetic recording system, and a magnetic layer or the like may be configured as an in-plane information recording medium. As a magnetic layer material suitable for heat-assisted recording, an FePt-based material may be used. Thereafter, by performing a “post heat treatment step”, the information recording medium is completed.

(Example)
Hereinafter, specific examples based on the glass substrate manufacturing method in the above embodiment will be described. FIG. 7 shows the crystal diameter of the crystallized glass, the specific elastic modulus, the polishing amount in the “second polishing step” of S17 (removal allowance: μm), and the roll-off value (nm) in each example and each comparative example. , Shows crystal seeds of crystallized glass, surface roughness (Å), HDD test result, drop impact test result, and glass composition. “1” to “5” of the glass composition in FIG. 7 indicate “Composition 1” to “Composition 5” in FIG.

  The crystal grain size (diameter) of the glass substrate was observed using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd. (JEOL)). The average particle size was n = 20. An arbitrary position of the glass substrate is observed, and the longest distance when the observed crystal is sandwiched between two parallel straight lines is set. The sample cut out the sample for transmission electron microscopes from the glass substrate before grinding | polishing.

  Since heat treatment of the glass substrate facilitates crystallization from the surface, the crystal grain size was measured on the glass substrate before polishing (after shape processing). The crystal seed | species produced | generated by the crystallization process was confirmed from the peak of diffraction intensity using the XRD apparatus (X-ray diffractometer) made from Rigaku.

  The specific elastic modulus is measured by Young's modulus using the elastic modulus measuring device JE-RT (manufactured by Nippon Techno Plus Co., Ltd.) by the bending resonance method, and the specific gravity is measured by the Archimedes method. The rate was calculated.

  The polishing amount (removal allowance: μm) was calculated by measuring the thickness of the glass substrate before and after polishing with a micrometer.

  As the roll-off value (RO), as shown in the cross section of FIG. 8, the distance RO at the position of r (mm) −0.5 (mm) = 32.0 mm was measured with OSA6320. For the planar shape profile of r = 22.0 mm to 31.7 mm, the closest straight line was obtained by the least square method, and it was defined as 0 line (straight line L). A negative roll-off value represents a sag with a size below the 0 line (straight line L). A positive roll-off value represents a so-called ski jump shape that rises above the 0 line (straight line L).

For the surface roughness (Ra: 1 μm ² ), the arithmetic average roughness Ra of the substrate surface in the range of 1 μm × 1 μm was measured using an AFM manufactured by Veeco. n = average of 10 pieces.

  In the HDD operation test, a magnetic recording layer was formed of a Co—Cr alloy on a glass substrate, and evaluation was performed based on the number of reading errors when operating to a position of r = 31.9 mm at 15000 rpm. The evaluation was performed by n = 100 sheets in each example and comparative example, and the total number of HDD test errors was counted.

  The number of errors 0 to 2 was evaluated as “A”. The number of errors was 3 to 5 and was evaluated as “B”. The number of errors 6 to 10 was evaluated as “F”. An error count of 11 or more was evaluated as “FF”.

  In the drop impact test, two glass substrates having a plate thickness t = 0.8 mm were mounted on the HDD device, and the HDD device was dropped from a height at which a predetermined impact value was obtained. The glass substrate was evaluated based on the presence or absence of cracks generated in the glass substrate.

  The impact value was 1300 G, and no crack was evaluated as “A”. The impact value was 1300 G, and 1 to 2 cracks were evaluated as “B”. The impact value was 1200 G, and one or more cracks were evaluated as “F”. The impact value was 1100 G, and one or more cracks were evaluated as “FF”.

In Example 1, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “A”, and the drop impact test result was evaluated “B”.

In Example 2, the crystal grain size of the glass substrate is “1” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “B”.

In Example 3, the crystal grain size of the glass substrate is “20” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated as “B”, and the drop impact test result was evaluated as “A”.

In Example 4, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “33.5” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “A”, and the drop impact test result was evaluated “B”.

In Example 5, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “36.5” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated as “B”, and the drop impact test result was evaluated as “A”.

In Example 6, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “5” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “2.5” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “B”.

In Example 7, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “40” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.5” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “B”.

In Example 8, the crystal grain size of the glass substrate is “20” nm, the specific elastic modulus of the glass substrate is “36.0” GPa · cm ³ / g, the polishing amount is “40” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.5” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated as “B”, and the drop impact test result was evaluated as “A”.

In Example 9, the crystal grain size of the glass substrate is “1” nm, the specific elastic modulus of the glass substrate is “33.5” GPa · cm ³ / g, the polishing amount is “5” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “2.5” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “B”.

In Example 10, the crystal grain size of the glass substrate is “1” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgTi ₂ O ₅ ” containing MgO—TgO ₂ -based crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 2”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “B”.

In Example 11, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgTi ₂ O ₅ ” containing MgO—TgO ₂ -based crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 2”. As a result, the HDD test result was evaluated “A”, and the drop impact test result was evaluated “B”.

In Example 12, the crystal grain size of the glass substrate is “20” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgTi ₂ O ₅ ” containing MgO—TgO ₂ based crystal, the surface roughness is “1.7” μm, and the glass composition is “Composition 2”. As a result, the HDD test result was evaluated as “B”, and the drop impact test result was evaluated as “A”.

In Example 13, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “ZnAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 3”. As a result, the HDD test result was evaluated “A”, and the drop impact test result was evaluated “B”.

In Example 14, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgTi ₂ O ₅ ” containing MgO—TgO ₂ -based crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 4”. As a result, the HDD test result was evaluated “A”, and the drop impact test result was evaluated “B”.

Comparative Example 1 does not use crystallized glass. The specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, the roll-off value is “−20” nm, the surface roughness is “1.7” μm, glass The composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “FF”.

In Comparative Example 2, the crystal grain size of the glass substrate is “25” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ −110 ”nm, the crystal seed is“ MgAl ₂ O ₄ ”containing spinel crystals, the surface roughness is“ 1.9 ”μm, and the glass composition is“ Composition 1 ”. As a result, the HDD test result was evaluated as “F”, and the drop impact test result was evaluated as “A”.

In Comparative Example 3, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “33.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” containing spinel crystals, the surface roughness is “1.7” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated “B”, and the drop impact test result was evaluated “F”.

In Comparative Example 4, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “37.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ −105 ”nm, the crystal seed is“ MgAl ₂ O ₄ ”containing spinel crystals, the surface roughness is“ 1.7 ”μm, and the glass composition is“ Composition 1 ”. As a result, the HDD test result was evaluated as “F”, and the drop impact test result was evaluated as “B”.

In Comparative Example 5, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “3” μm, and the roll-off value is “ The crystal seed is “MgAl ₂ O ₄ ” including spinel crystals, the surface roughness is “3.2” μm, and the glass composition is “Composition 1”. As a result, the HDD test result was evaluated as “F”, and the drop impact test result was evaluated as “F”.

In Comparative Example 6, the crystal grain size of the glass substrate is “10” nm, the specific elastic modulus of the glass substrate is “35.0” GPa · cm ³ / g, the polishing amount is “45” μm, and the roll-off value is “ −110 ”nm, the crystal seed is“ MgAl ₂ O ₄ ”containing spinel crystals, the surface roughness is“ 1.5 ”μm, and the glass composition is“ Composition 1 ”. As a result, the HDD test result was evaluated as “F”, and the drop impact test result was evaluated as “B”.

In Comparative Example 7, the crystal grain size of the glass substrate is “50” nm, the specific elastic modulus of the glass substrate is “51.0” GPa · cm ³ / g, the polishing amount is “20” μm, and the roll-off value is “ −240 ”nm, the crystal seed is“ MgSiO ₃ ”, the surface roughness is“ 3.4 ”μm, and the glass composition is“ Composition 5 ”. As a result, the HDD test result was evaluated as “FF”, and the drop impact test result was evaluated as “F”.

  From the results of the above examples and comparative examples, by setting the crystal grain size of the glass substrate to 1 nm or more and 20 nm or less, polishing is performed without reducing the polishing rate, and roll-off deterioration during polishing is suppressed. .

In addition, by the specific elastic modulus of the glass substrate to 33.5GPa · ^cm 3 / g or more 36.5GPa · cm ³ or less in the range, to suppress the roll-off deterioration, it is possible to secure the strength characteristics. When the specific elastic modulus is less than 33.5 GPa · cm ³ / g, the specific elastic modulus is too low to obtain a desired strength. When the specific modulus exceeds 36.5 GPa · cm ³ , the specific modulus is too high, the polishing rate is deteriorated, and the roll-off is further deteriorated.

  If the machining allowance in the polishing step is less than 5 μm on one side, the roughness in the shape processing step remains and desired strength characteristics cannot be obtained. If the machining allowance in the polishing process exceeds 40 μm on one side, roll-off will deteriorate.

  When the roll-off value is less than −100 nm or 30 nm or more, the inclination of the end shape is too large, and the head cannot follow the glass substrate shape. As a result, the flying height of the head becomes unstable, and read / write errors are likely to occur.

In the case of crystallized glass containing spinel (MgAl ₂ O ₄ , ZnAl ₂ O _4, etc.) or MgO-TgO ₂ -based crystals, the crystal grain size can also be suppressed, and the surface roughness can be reduced. Is also effective.

Glass composition ranges are 54 wt% or more and 64 wt% or less for SiO ₂ , Al ₂ O ₃ is 12 wt% or more and 22 wt% or less, B ₂ O ₃ is 1 wt% or more and 8 wt% or less, and Na ₂ O is 1 wt%. More than 8 wt%, MgO 5 wt% or more and 15 wt% or less, and TiO ₂ outside the range of 1 wt% or more and 8 wt% or less, it becomes difficult to make the crystal grain size 20 nm or less. It becomes difficult to achieve an elastic modulus of 33.5 GPa · cm ³ / g or more and 36.5 GPa · cm ³ or less.

  As described above, in the present embodiment, it is possible to obtain a method for manufacturing a glass substrate for an information recording medium capable of suppressing the occurrence of roll-off and ensuring a smooth area on the main surface as compared with the conventional case. . As a result, even when the obtained glass substrate is used in an HDD device, it is possible to provide a glass substrate for an information recording medium capable of suppressing the occurrence of read / write errors and obtaining a higher recording density. To do.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Glass substrate, 2, 3 Main surface, 4 Inner peripheral end surface, 4a, 6a Linear part, 4b, 6b Chamfer part, 5,15 Hole, 6 Outer peripheral end surface, 10 Information recording medium, 12 Compressive stress layer, 14 Magnetic recording Layer, 20 housing, 21 head slider, 22 suspension, 23 arm, 24 vertical axis, 25 voice coil, 26 voice coil motor, 27 clamp member, 28 fixing screw, 30 information recording device.

Claims (4)

A method for producing a glass substrate for an information recording medium, wherein crystallized glass is used for the glass substrate,
A molding step of molding the glass substrate;
A shape processing step for performing shape processing on the glass substrate following the forming step,
Following the shape processing step, a polishing step for polishing the surface of the glass substrate;
With
The crystal grain size of the glass substrate before the polishing step is 1 nm or more and 20 nm or less,
The polishing amount of the surface in the polishing step is 5 μm or more and 40 μm or less,
The specific elastic modulus of the glass substrate is less than or equal 33.5GPa · ^cm 3 / g or more 36.5GPa · cm ^3, information method of manufacturing a glass substrate for a recording medium.   The radius of the glass substrate after performing the polishing step is defined as r (mm), and the roll-off value at a position of r (mm) −0.5 (mm) is −100 (nm) or more and 30 ( nm) or less, the method for producing a glass substrate for an information recording medium according to claim 1. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the glass substrate is a crystallized glass containing spinel crystals or a crystallized glass containing MgO—TgO ₂ crystals. The glass substrate has a glass composition range of SiO ₂ from 54 wt% to 64 wt%, Al ₂ O ₃ from 12 wt% to 22 wt%, B ₂ O ₃ from 1 wt% to 8 wt%, Na ₂ 4. The information recording medium according to claim 1, wherein O is 1 wt% or more and 8 wt% or less, MgO is 5 wt% or more and 15 wt% or less, and TiO ₂ is 1 wt% or more and 8 wt% or less. A method for producing a glass substrate.

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